Known from German patent DE 19651362 C1 is a measuring device for fill-level monitoring having an oscillatory system, which is composed of two rods. In such case, an inner oscillatory rod is surrounded coaxially by an outer tubular oscillatory rod. Each of the oscillatory rods is secured via an elastic holding part to a shared carrier and are excited to execute opposite transverse oscillations with the eigenresonance frequency of the oscillatory system. The measuring device is mounted on a container in such a manner that the outer oscillatory rod contacts the fill substance as soon as such reaches the fill level to be monitored. Serving as measured variable for fill level detection is the oscillation amplitude.
In order to assure a decoupled oscillation in the case of accretion formation, the inner oscillatory rod includes a compensation mass, which is shiftably arranged, so that the resonant frequency of the inner oscillatory structure is adaptable to that of the outer oscillatory structure. The compensation mass is secured, for example, on an axially extending rod, which has a screw thread. A motor rotates the rod in such a manner that the compensation mass moves in the axial direction.
Described in Offenlegungsschrift (laid open application) EP 2273239 A1 is a fill level measuring apparatus, which likewise has two tubular oscillatory bodies arranged in one another. The outer oscillatory body is secured to a securement system via an elastic section. Arranged in the interior of the inner oscillatory body is a tuning body. The tuning body is sectionally elastically embodied and placed under compression in the inner oscillatory body. Furthermore, the tuning body includes a section with an external thread, which is matched to an internal thread in the inner wall of the inner oscillatory body. For adjusting the position of the tuning body, a frontal slot is provided, in which a displacement instrument, for example, a screw driver, can engage. The adjusting occurs manually or via a motor driven control.
A manual adjusting of the tuning body via the rod-shaped displacement instrument is uncomfortable. A motor control, in contrast, is complicated to put into practice. Furthermore, the described oscillatory system is relatively complicated to manufacture, because of the screw thread.
An object of the invention is to provide a fill-level measuring device having an easily displaceable tuning body.